Quote: (Originally Posted by
warjarrett)
If I dive this week to 45 ft (15m) for 1 hour at fixed 0.7 PO2, then exactly the same dive next week but at 1.4 PO2 (assume I spend very little time ascending or descending), how will my gas consumption of O2 and air/dil compare? In other words, will my body absorb more O2 and/or more dil during either of these 2 dives? Will I have to add or release any more O2 and/or dil during either of these 2 dives? Please explain your answer.
Hello,
Oxygen consumption is driven by metabolic need, not the PO2 available, so assuming your dives are identical in every way other than the gas changes you specified, oxygen consumption will not change. Nor will you absorb more oxygen. While the arterial PO2 will be higher on the dive with a set point of 1.4, the PO2 in the tissues themselves will not change because the oxygen is metabolised. The hemoglobin may unload a little less oxygen, and the venous hemoglobin may be slightly more saturated with oxygen on the 1.4 dive than the 0.7 dive.
As has been pointed out, absorption of inert gas is driven by the partial pressure, which is higher on the 0.7 dive: therefore you will absorb more nitrogen. However, the total difference in volume absorbed will be sufficiently small that you will not notice it on your dil pressure gauge.
Warm regards,
Simon M